Silicon oxide (SiO2) finds extremely widespread use in the fabrication of semiconductor devices. Important applications for SiO2 films include providing gate dielectric structures for MOS transistor devices, and providing electrical isolation between electrically conducting metal lines in an integrated circuit.
One approach for forming silicon oxide films on a semiconductor substrate is through the process of chemical vapor deposition (CVD). Specifically, chemical reaction between a silicon supplying material and an oxygen supplying material results in deposition of solid phase silicon oxide on top of a semiconductor substrate.
Organosilane silicon supplying materials including at least one Sixe2x80x94C bond are often utilized during CVD of silicon oxide. As a result of the carbon present in such a silicon supplying material, carbon-doped silicon carbon oxide (SiCxOy) can be formed, for example, through the following chemical reactions:
SiH(CH3)3(gas)+O3(gas)+(heat or UV)xe2x86x92SiCxOy(solid)+H2O+CO2
SiH(CH3)3(gas)+O2(gas)+RF (plasma)xe2x86x92SiCxOy(solid)+H2O+CO2
The reactant species SiH(CH3)3 is trimethylsilane (xe2x80x9cTMSxe2x80x9d). Other organosilane compounds include dimethylsilane, diethylsilane, diacetoxyditertiarybutoxysilane, and 2,4,6,8-tetramethyltetrasiloxane.
As a result of CVD chemical reactions involving organosilane process gases, carbon at concentrations of at least about 8 atomic percent and greater may be incorporated into the silicon oxide film. Incorporation of carbon at these quantities into the silicon oxide during deposition has several effects. First, carbon favorably enhances the dielectric properties of the resulting film. Second, the presence of carbon softens the freshly deposited film, rendering the it more sensitive to handling stress.
Water is one by-product of the CVD reaction to form carbon-doped silicon oxide. Water can be incorporated into the deposited film as an Sixe2x80x94OH chemical bond, or physically absorbed into the film as moisture. This Sixe2x80x94OH bond or moisture is not part of stable carbon-doped silicon oxide film, and may later cause failure of dielectric material during device operation.
Accordingly, undesirable chemical bonds such as Sixe2x80x94OH are typically removed from a deposited carbon-doped silicon oxide film through the process of densification. Conventional densification steps subject the deposited carbon-doped silicon oxide film to a high temperature anneal. The energy from this anneal replaces unstable, undesirable chemical bonds with more stable bonds characteristic of an ordered silicon oxide film, increasing the density of the film.
The conventional thermal anneal step is of relatively long duration (approx. 30 min-2 hrs.) This thermal anneal thus consumes significant processing time and slows down the overall fabrication process.
In order to maintain high throughput, thermal annealing steps of long duration are performed in batch-type furnace devices having a high wafer capacity, wherein a large number of wafers are supported by their edges in slots in the walls of the furnace. However, as stated above carbon-doped silicon oxide films are soft and easily damaged by insertion and removal from conventional batch-type furnaces. This prevents wafers coated with the films from being annealed in large quantities.
Therefore, there is a need in the art for a process for densifying CVD carbon-doped silicon oxide films which requires a minimum of water handling and which consumes a minimum of processing time.
It has been suggested to utilize ultraviolet radiation to aid in the densification of CVD silicon oxide films. However, conventional ultraviolet radiation sources typically emit radiation at a single wavelength corresponding to the excited energy state of electrons from a single excited gas species. However, it may be useful to utilize ultraviolet radiation having a plurality of wavelengths.
Therefore, there is a need in the art for a radiation source which simultaneously emits ultraviolet radiation of a combination of different energies and intensities.
One embodiment of the present invention relates to the use of ultraviolet radiation to anneal and densify a CVD carbon-doped silicon oxide film. Specifically, a freshly deposited carbon-doped silicon oxide film is exposed to ultraviolet radiation calculated to disrupt undesirable chemical bonds, replacing these bonds with more stable bonds characteristic of an ordered silicon oxide film. As a result of this UV radiation exposure, undesirable chemical bonds in the film such as Sixe2x80x94OH are broken, and gas is evolved. This gas is then removed to leave a densified and stable deposited carbon-doped silicon dioxide film.
A first embodiment of an ultraviolet radiation source in accordance with the present invention comprises a first gas supply in fluid communication with an airtight bulb through a first mass flow controller, the first mass flow controller operable to regulate a flow of a first gas into the bulb. A second gas supply is in fluid communication with the bulb through a second mass flow controller, the second mass flow controller operable to regulate a flow of a second gas into the bulb. A pump is operable to evacuate the bulb through an outlet. A filament is disposed within the bulb and in electrical communication with a power supply. Current flowed through the filament causes the first gas and the second gas to become excited and emit ultraviolet radiation having a combination of wavelengths and intensities.
A first embodiment of a method of controlling an energy and an intensity of radiation output from a radiation source comprises the step of electrically stimulating a first gas and a second gas present in an airtight bulb, such that the first gas emits radiation at a first energy and a first intensity, and the second gas emits radiation at a second energy and a second intensity.